Audio line isolator

ABSTRACT

A method for isolating suites includes the steps of isolating the suites when an alarm is initiated, setting a timer during isolation creating a window of time to clear a short circuit, clearing said short circuit, removing isolation from the suites as the timer reaches completion, determining if there is a short circuit in each of the suites, and isolating suites that have a short circuit.

FIELD OF THE INVENTION

[0001] The present invention relates generally to audio line isolators.More particularly, the present invention relates to multiple suite audioline isolators.

BACKGROUND OF THE INVENTION

[0002] Section 3.2.4.19.10 of the Canadian National Building Code statesthat damage to or disconnection of an audible signal device in adwelling unit may not interfere with the ability of devices outside thedwelling unit to sound an alarm.

[0003] Existing line isolation devices designed to serve this functionin systems using 70 v audio signaling have significant reaction times,require the presence of audio on power-up to perform fault isolation,and require the presence of an audio signal to maintain isolation. Theselimitations make the existing designs unacceptable for use withamplifiers which have fault sensing capabilities.

[0004] Existing designs presently use Polymeric Positive TemperatureCoefficient devices, otherwise known as PPTCs, to provide passiveisolation of short circuit conditions on audio lines. These devices arethermal in nature, requiring the initial presence of high values ofcurrent on the audio line before any isolation can take place. The lowercurrent values associated with 70 v audio and the significantly longreaction times inherent in the nature of PPTCs make them unsuitable foruse in this application.

[0005] The thermal nature of PPTCs also results in significantsensitivity to ambient temperature conditions. Trip and hold currentsfor PPTCs typically used in this application are derated as much as 25%over the 0 to 49° C. rated temperature range.

SUMMARY OF THE INVENTION

[0006] The present invention operates to perform isolation independentof temperature effects over its rated range.

[0007] The device uses a low value resistance in parallel with thedetector of an optoisolator to sense peak current values and subsequentloading being presented by the audio signaling devices in a dwellingunit. When the peak current value exceeds a point dictated by the valueof the resistor, the output side of the optoisolator becomes active.This activity is sampled and initiates activation of a relay used toisolate the dwelling unit from the audio circuit. Activation of the coilof the relay for approximately 500 uS initiates electronic latching ofthe isolation relay. Subsequent isolation is independent of the presenceof audio, resulting in a device which has a very fast reaction time, andhas no reliance on the continued presence of an audio signal to maintainisolation.

[0008] An audio amplifier which has fault sensing capabilities willtypically not attempt to supply audio into a short circuit condition. Atiming circuit is incorporated into this design to activate theisolation relays for the first 2.7 seconds on presentation of the alarm.Momentary clearance of any short that may have been present gives anamplifier with short sensing capabilities a window of opportunity tosupply audio. This audio will subsequently be used by the isolator toperform sensing when the timer circuit releases control of the isolationrelay.

[0009] Supervision switching is designed to be compatible with class Aor class B supervision, and allows the use of a single sensing andisolating element to monitor for short circuit conditions in thedwelling unit.

[0010] In one embodiment of the invention, a method for isolating suitesincludes the steps of isolating the suites when an alarm is initiated,setting a timer during isolation creating a window of time to clear ashort circuit, clearing the short circuit, removing isolation from thesuites as the timer reaches completion, determining if there is a shortcircuit in each of the suites, and isolating suites that have a shortcircuit.

[0011] In another embodiment of the invention, a line isolator formultiple suites includes a supervisory relay capable of supplying powerto suites in series and in parallel, and an isolation relay incommunication with the supervisory relay. The isolation relay preventspower from being supplied to a suite. Sense circuitry is incommunication with the isolation relay. The sense circuitry determinesif there is a short circuit. Latching circuitry is in communication withthe sense circuitry. The latching circuitry activates the isolationrelay to prevent power from being supplied to a suite when the sensecircuitry determines the occurrence of a short circuit. A timer is incommunication with the latching circuitry. The timer allows time for ashort circuit to be cleared during isolation.

[0012] In an alternate embodiment, a line isolator system for multiplesuites includes a supervisory relay means for supplying power to suitesin series and in parallel and an isolation relay means for preventingpower from being supplied to a suite. The isolation relay means is incommunication with the supervisory relay means. A sense circuitry meansis provided for determining if there is a short circuit and is incommunication the isolation relay means. A latching circuitry means isprovided for activating the isolation relay means to prevent power frombeing supplied to a suite when the sense circuitry means determines theoccurrence of a short circuit. The latching circuitry means is incommunication with the sense circuitry means. A timer means is providedfor creating a time period during isolation to allow a short circuit tobe cleared. The timer means is in communication with the latchingcircuitry means.

[0013] There has thus been outlined, rather broadly, the more importantfeatures of the invention in order that the detailed description thereofthat follows may be better understood, and in order that the presentcontribution to the art may be better appreciated. There are, of course,additional features of the invention that will be described below andwhich will form the subject matter of the claims appended hereto.

[0014] In this respect, before explaining at least one embodiment of theinvention in detail, it is to be understood that the invention is notlimited in its application to the details of construction and to thearrangements of the components set forth in the following description orillustrated in the drawings. The invention is capable of otherembodiments and of being practiced and carried out in various ways.Also, it is to be understood that the phraseology and terminologyemployed herein, as well as the abstract included below, are for thepurpose of description and should not be regarded as limiting.

[0015] As such, those skilled in the art will appreciate that theconception upon which this disclosure is based may readily be utilizedas a basis for the designing of other structures, methods and systemsfor carrying out the several purposes of the present invention. It isimportant, therefore, that the claims be regarded as including suchequivalent constructions insofar as they do not depart from the spiritand scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a schematic of a dual suite audio line isolator.

[0017]FIG. 2 is a schematic of a dual suite audio line isolator insupervisory mode.

[0018]FIG. 3 is a schematic of a dual suite audio line isolator in alarmmode.

[0019]FIG. 4 is a flow diagram illustrating the steps that may befollowed in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0020]FIG. 1 is a schematic of a dual suite audio line isolator. Theisolator includes circuitry sufficient to perform supervision, shortcircuit sensing, and fault isolation for the audio circuitry in two ormore separate dwelling units or suites. The dual suite audio lineisolator illustrated in FIG. 1 includes timer circuitry, suite 1 andsuite 2 latching circuitry, suite 1 and suite 2 sensing circuitry, suite1 and suite 2 isolation relay contacts, and suite 1 and suite 2supervision relay contacts. As illustrated in FIG. 1, sensing andisolation circuitry for each suite can be identical.

[0021] In an alarm situation the timing circuitry is initiated. Thetiming circuit includes a dual comparator with open collector outputs(U2) as well as a capacitor C1, and resistors R3, R4, and R5. ResistorsR4 and R5 form a voltage divider which provides the positive inputs tothe comparators with a reference of approximately 5 v. C1 and R3 form anR-C timing constant, so that the initial voltage at the negative inputsto the comparators is above the fixed 5 v reference, ramping down tosink below the reference voltage after approximately 2.7 seconds haveelapsed. The comparators sink current during this time, activating theisolation relays for the first 2.7 seconds on presentation of alarm.Activating isolation for a short period on presentation of the alarmstate clears any short circuit condition that may have been presentwhile the system was in its supervisory state. If an amplifier withshort circuit sensing capability is being used to supply audio, theimplementation of a timer circuit to provide initial momentary isolationon presentation of alarm will allow the amplifier to provide audio. Whenthe start up isolation ends, the device will use this audio to sense anysupervisory short that may have been present.

[0022] Current sensing on the audio line is performed by R1 (R12) and U1(U3) (elements in parenthesis refer to identical elements in suite 2).D4 (D8) is present to protect the detector LED of U1 (U3) during reversebiasing, and R2 (R13) is present to provide a measure of currentlimiting for both diodes. R1 (R12) and the detector portion of U1 (U3)acts as a current controlled switch. Audio current flowing through R1(R12) causes a voltage drop to be developed across the resistor. Whencurrent through this resistor is of sufficient magnitude to cause a peakvoltage drop of ±1.5V, current is pulsed through the detector portion ofU1 (U3), allowing subsequent pulse of current through the transistorportion of U1 (U3). The use of a resistor as the sense element allowsthe sensitivity of the device to be changed by changing the value of theresistor. This approach also allows higher sensitivity than was possiblewith previous designs, which is a major advantage given the low currentvalues associated with 70 v audio. The resistance value incorporated inthis application causes the detector portion of the optoisolator tobecome active on presentation of approximately 75 mA RMS. This resultsin isolation of a suite if it presents greater than 5 Watts of load tothe audio signal circuit.

[0023] C3 (C6), R11 (R19), and R6 (R14) perform a short duration sampleand hold action on the current pulsing of the transistor portion of U1(U3). R11 (R19) limits the peak output current of U1 (U3) toapproximately 2 mA. This current will charge C3 (C6) to 0.65V within 3.5uS, at which point the base current of Q1 (Q3), the driver for theisolation relay, becomes significant. The time period required for C3(C6) to totally discharge through R11 (R19) is approximately 5 mS.

[0024] The isolation relay K2 (K4) is latched into its active state byQ2 (Q4) and associated biasing. Activation of latching by the start-uptimer is disabled by D6 (D10). When the sense circuit activates Q1 (Q3),current is drawn through the coil of the isolation relay (K2) toinitiate activation of the relay. Current is also drawn through thebiasing network for the base of Q2 (Q4) through R10 (R18). The values ofR10 (R18), R8 (R16), and C4 (C7) are such that Q2 (Q4) will begin toturn on when Q1 (Q3) has been active for 500 uS. Activating Q2 (Q4)drives current through R9 (R17). When the voltage developed through R9(R17) reaches approximately 1.4V, current is diverted through the baseof Q1 (Q3) via D5 (D9), latching Q1 (Q3) on to complete activation ofthe isolation relay. From this point The isolation relay will remainactive

[0025] When the latching sequence is completed, isolation of the faultbecomes independent of the audio signal. This is not the case forprevious designs, which require hold current. The audio need only bepresent for approximately 500 uS for latching to be successfullycompleted, allowing this device to be used with audio amplifiers thathave relatively high speed fault sensing capability. The amplifier maysense the fault and disable its output within the 10 mS it takes for theisolation relay to act, but as long as audio was present for the 500 uSrequired for sensing and latching, the device will clear the fault. Thefact that there is no requirement for hold current on the isolated linemakes this design highly suitable for intermittent signals such asvoice.

[0026] Fire alarm signal circuits are required to be supervised forshort circuit and open circuit conditions. This is typically achieved bydevising switching so that connection to all devices are in series whenthe circuit is in its normal, or supervisory state, and connection toall devices are in parallel when the circuit is in its active, or alarmstate. In audio applications, all signaling devices are capacitivelycoupled, so by installing a known resistance at the end of the circuit,application of a known DC current during supervision allows shortcircuit and open circuit conditions to be sensed by the control panel.The DC circuit used to supply the device is also a supervised circuit.Supervision of the DC circuit used to supply the device is accomplishedby providing supervision current of polarity opposite to the supplypolarity required to power the device during alarm. D1 provides thesupervisory switching by preventing the flow of current into the DCportion of the device during supervision.

[0027] There are two classes of supervision; class A and class B. Inclass A operation the end of the circuit and end of line resistor arebrought back to a second set of outputs. In this way, when a single opencircuit condition is present the entire circuit can still be actuatedduring alarm by using both sets of outputs. In class B operation, onlyone set of outputs is used, so that an open or short can be detected,but the portion of the circuit beyond the open cannot be actuated duringalarm. The present invention is suitable for use as an audio lineisolator in either class A or class B circuits.

[0028]FIG. 2 illustrates supervisory DC current routing for the audioportion of the device. Positive current is input from the alarm panel isvia TB 1-2. Positive current output to suite 1 is via TB2-7. Return ofpositive current from suite 1 is via TB2-5. Positive current output tosuite 2 is via TB2-3. Return of positive current from suite 2 is viaTB2-1. Positive current output to the next device or end of lineresistor is via TB 1-4. Negative current input is via TB1-1. Negativecurrent output to suite 1 is via TB2-8. Return of negative current fromsuite 1 is via TB2-6. Negative current output to suite 2 is via TB2-4.Return of negative current from suite 2 is via TB2-2. Negative currentoutput to the next device or end of line resistor is via TB 1-3.

[0029] Positive and negative supervisory inputs for the DC portion ofthe circuit are provided by TB1-6 and TB1-5 respectively. Positive andnegative supervisory outputs to the next device or end of line resistorare provided by TB 1-8 and TB 1-7 respectively.

[0030] In practical terms, supervision typically requires that there betwo possible paths for the supply of power to a signaling device duringalarm. The fact that there are two possible supply paths implies thatboth of these paths must be monitored and opened for successfulisolation. In this design, the supervision switching for the audiocircuit has been modified by the use of the normally closed contact ofK1 a (K3 a) so that the supervisory path is still valid, but there isonly one supply path to the signaling device during alarm. Thismodification allows the use of a single sensing and isolating element tomonitor for short circuit conditions and apply isolation during alarm,rather than the two sensing and isolating elements that would otherwisebe required.

[0031] As illustrated in FIG. 3, alarm conditions are presented to thedevice from the control panel by presenting 24 vDC to TB 1-5 and TB 1-6,then presenting 70 vRMS audio to TB1-1 and TB1-2. Presentation of 24 vDCat TB1-5 with respect to TB1-6 forward biases D1, providing supplycurrent to the device and activating supervision relays K1 and K3. Thisplaces the field wiring to the suites in parallel, but opens the supplypath to suite 1 at TB2-8, and the supply path to suite 2 at TB2-4. Asmentioned above, opening these supply paths allows the use of a singlesensing element and point of isolation for each suite. It is noted thatthe present invention is not limited for use with only 70 vRMS audioapplications, but can be used in other applications such as 25 vRMS orDC circuit applications.

[0032] Note that in the case of an amplifier with fault sensingcapabilities the DC alarm signal presentation should occur at the sametime as, or slightly after presentation of the audio alarm signal.Sequencing the alarm presentation in this order allows the amplifier totake full advantage of the start up timer explained below. The devicecan be used with an amplifier that has no fault sensing capabilities,but DC alarm signal presentation must take place before the presentationof the audio alarm, since presentation of the audio will damage thedevice if it is de-energized and a short circuit condition is present.This device can be used with either type of amplifier, by appropriatelyordering the sequence of alarm signal presentation.

[0033]FIG. 4 is a flow diagram of the method steps of the invention. Instep 1 an alarm is initiated by input to the panel. Examples of eventswhich could initiate an alarm include the activation of a pull station,or input from a smoke detector.

[0034] In step 2 if there is no audio short is present the logic willcontinue to steps 3 through 5. Steps 3 through 5 represent the sequenceof events if the short was not present. If a short is present the logicwill continue to steps 6 through 17. Steps 6-17 represent the sequenceswhich could take place if there was a short circuit condition present onthe audio circuit in supervision.

[0035] In step 3 since there is no short present on the audio circuit,the audio amplifier will power up normally and supply audio to thecircuit. The DC circuit is the power supply for the isolators. Enablingthis circuit activates the isolators and initiates the startup timersreferred to in step 4.

[0036] In step 4, the startup timers are initiated on activation of theisolators in the previous step. This results in isolation of all suitesregardless of the presence of a short circuit condition.

[0037] In step 5, as the timer on each isolator in the circuit reachescompletion, isolation is removed from the suites that the isolator ismonitoring. This allows audio to be provided to the suites. Given thatthere was no short circuit condition present, all suites are providedwith audio. The actual sensing of short circuit conditions by theisolators is not relevant for the sequence represented by steps 3through 5 of the flowchart.

[0038] Steps 6 through 17 represent the sequences which will take placeif there was a short circuit condition present on the audio circuit insupervision. In step 6, the audio amplifier has sensed that a shortcircuit condition was present before the initiation of the alarm. Theamplifier subsequently does not provide audio, and continues monitoringof the circuit for clearance of the short. The DC circuit is the powersupply for the isolators. Enabling this circuit activates the isolatorsand initiates the startup timers referred to in step 7.

[0039] In step 7, the startup timers are initiated on activation of theisolators in the previous step. This results in isolation of all suitesregardless of the presence of a short circuit condition. Isolationregardless of the presence of a short circuit is significant here, sincethe isolator requires the presence of an audio signal to perform shortcircuit detection. The previous step illustrated that audio will notinitially be present if a short circuit condition was present duringsupervision.

[0040] In step 8 isolation of all suites in the previous step clearedthe short circuit condition despite the fact that there was no audiopresent for the isolators to use for sensing. This initial isolationgives the audio amplifier a window of opportunity to provide audio forthe isolators to subsequently use for sensing.

[0041] In step 9, the isolation of all suites initiated in step 7 timesout after approximately 2.7 seconds. At this point, the short that wascleared by the timers is momentarily re-asserted.

[0042] In step 10, the isolator responsible for monitoring the suite onwhich the short is present uses the audio signal to sense the short.Isolation is initiated and the latching circuitry for the affected suiteensures that isolation of the suite is carried to completion regardlessof subsequent presence of the audio signal.

[0043] In step 11 depending on how robust the audio signal is and thecharacteristics of the monitoring circuitry in the audio amplifier, theamplifier may sense the short that was re-asserted in step 9 before theisolator can carry isolation of the suite to completion. Steps 14through 17 outline the sequence of events followed if the amplifiersenses the short before the isolator can actuate the isolation relay.

[0044] In step 12, isolation is carried to completion withinapproximately 10 milliseconds of initial sensing of the short. Steps 12and 13 represent the sequence of events followed if the sense circuitryin the audio amplifier was not fast enough to sense the re-assertedshort before the isolator could sense the short and complete isolation.

[0045] In step 13, the short circuit condition has now been successfullyisolated, and the audio circuit is operating normally to supply audio toall suites except the one on which the short was present.

[0046] Steps 14 through 17 outline the sequence of events followed ifthe amplifier senses the short before the isolator can actuate theisolation relay. In step 14, the short circuit condition has been sensedby the amplifier, and audio has subsequently been shut down. Theisolators latching circuitry ensures that isolation is carried tocompletion despite the fact that audio is no longer present on thecircuit.

[0047] In step 15, isolation of the short is carried to completion bythe latching circuitry of the isolator. At the end of this step thecause of the short circuit condition has been isolated.

[0048] In step 16 shortly after isolation of the short circuit conditionis completed by the isolator, the amplifier senses that there is nolonger a short circuit condition present.

[0049] In step 17, having sensed that there is no longer a short circuitcondition present on the audio circuit, the amplifier re-applies audio.The short circuit condition has now been successfully isolated, and theaudio circuit is operating normally to supply audio to all suites exceptthe one on which the short was present.

[0050] The many features and advantages of the invention are apparentfrom the detailed specification, and thus, it is intended by theappended claims to cover all such features and advantages of theinvention which fall within the true spirits and scope of the invention.Further, since numerous modifications and variations will readily occurto those skilled in the art, it is not desired to limit the invention tothe exact construction and operation illustrated and described, andaccordingly, all suitable modifications and equivalents may be resortedto, falling within the scope of the invention.

What is claimed:
 1. A method for isolating suites comprising the stepsof: isolating the suites when an alarm is initiated; setting a timerduring isolation creating a window of time to clear a short circuit;clearing said short circuit; removing isolation from the suites as thetimer reaches completion; determining if there is a short circuit ineach of the suites; and isolating suites that have a short circuit. 2.The method as recited in claim 1 further comprising the step ofsupplying the suites with supply power through a single power supplypath when said alarm is initiated.
 3. The method as recited in claim 1further comprising the step of determining if a short circuit waspresent before said alarm was initiated.
 4. The method as recited inclaim 3 further comprising the step of disabling audio if a shortcircuit was present before said alarm was initiated.
 5. The method asrecited in claim 1 further comprising the step of determining if therewas an audio short before said alarm was initiated.
 6. The method asrecited in claim 1 further comprising the step of providing supply powerto the suites in series before said alarm is initiated and providingsupply power to the suites in parallel after said alarm is initiated. 7.The method as recited in claim 1 further comprising the step of using aresistor to determine if there is a short circuit in each of the suitesafter the timer has timed out.
 8. The method as recited in claim 1further comprising the step of using a resistor to determine if there isan audio short circuit in each of the suites after the timer has timedout.
 9. A line isolator for multiple suites comprising: a supervisoryrelay capable of supplying power to suites in series and in parallel; anisolation relay in communication with said supervisory relay whereinsaid isolation relay prevents power from being supplied to a suite;sense circuitry in communication with said isolation relay wherein saidsense circuitry determines if there is a short circuit; latchingcircuitry in communication with said sense circuitry wherein saidlatching circuitry activates said isolation relay to prevent power frombeing supplied to a suite when said sense circuitry determines theoccurrence of a short circuit; and a timer in communication with saidlatching circuitry wherein said timer allows time for a short circuit tobe cleared during isolation.
 10. The line isolator as recited in claim 9wherein said supervisory relay supplies power to said suites using onlyone supply path during an alarm situation.
 11. The line isolator asrecited in claim 9 wherein said sense circuitry comprises a resistor asa sense element.
 12. The line isolator as recited in claim 9 furthercomprising an audio disabler in communication with said sense circuitrywherein said audio disabler disables audio if a short circuit is sensedbefore an alarm is initiated.
 13. The line isolator as recited in claim9 further comprising an audio disabler in communication with said sensecircuitry wherein said audio disabler disables audio if an audio shortcircuit is sensed before an alarm is initiated.
 14. The line isolator asrecited in claim 9 wherein said supervisory relay supplies power to thesuites in series before an alarm is initiated and supplies power to thesuites in parallel after the alarm is initiated.
 15. A line isolatorsystem for multiple suites comprising: a supervisory relay means forsupplying power to suites in series and in parallel; an isolation relaymeans for preventing power from being supplied to a suite, saidisolation relay means in communication with said supervisory relaymeans; a sense circuitry means for determining if there is a shortcircuit wherein said sense circuitry means is in communication saidisolation relay means; a latching circuitry means for activating saidisolation relay means to prevent power from being supplied to a suitewhen said sense circuitry means determines the occurrence of a shortcircuit wherein said latching circuitry means is in communication withsaid sense circuitry means; and a timer means for creating a time periodduring isolation to allow a short circuit to be cleared wherein saidtimer means is in communication with said latching circuitry means. 16.The line isolator system as recited in claim 15 wherein said supervisoryrelay supplies power to said suites using only one supply path during analarm situation.
 17. The line isolator system as recited in claim 15wherein said sense circuitry comprises a resistor as a sense element.18. The line isolator system as recited in claim 15 further comprisingan audio disabler in communication with said sense circuitry whereinsaid audio disabler disables audio if a short circuit is sensed beforean alarm is initiated.
 19. The line isolator system as recited in claim15 further comprising an audio disabler in communication with said sensecircuitry wherein said audio disabler disables audio if an audio shortcircuit is sensed before an alarm is initiated.
 20. The line isolatorsystem as recited in claim 15 wherein said supervisory relay suppliespower to the suites in series before an alarm is initiated and suppliespower to the suites in parallel after the alarm is initiated.